Fig. 3: Focus on the two main Cenozoic warm periods, with additional data pertaining to the Southern Ocean.

The MMCO is on the left and the EECO is on the right. a,b, SST compilation along with the benthic δ¹⁸O compilation⁸, as in Fig. 2. These data indicate, during the climate optima, reductions in the temperature difference between low-latitude and high-latitude surface waters. c,d, FB-δ¹⁵N difference between Pacific and Atlantic core sites (Δδ¹⁵N_P-A), as in Fig. 2. In c and d, other lines indicate running averages of the δ¹⁸O difference between benthic and surface-dwelling planktic foraminifers (Δδ¹⁸O) in the Southern Ocean (c, ODP Site 1171, red line^37,38; d, ODP Sites 690 and 738, purple lines (ref. ⁴¹ and references therein)). These data suggest a weaker vertical density gradient in the Southern Ocean during the climate optima, consistent with stronger ventilation of the deep ocean from the Southern Ocean surface. e,f, FB-δ¹⁵N records for these time intervals. In e, the lines indicate the average records of species-specific FB-δ¹⁵N from ODP Site 872 (green) and DSDP Site 516 (blue). Hatched bars indicate sedimentation hiatuses in the Southern Ocean, which have been attributed to stronger deep-water circulation³⁹. In f, the lines indicate the average records of mixed-taxa FB-δ¹⁵N in Site 1209 (light green) and Site 1263 (light blue)¹⁸, as in Fig. 2. New species-specific FB-δ¹⁵N data from Site 516 are in dark blue. Pal, Palaeocene; S. Ocean, Southern Ocean.